Laboratory and Field-Based Tests of Deltamethrin Insecticides Against Adult Culicoides Biting Midges

Abstract

Bluetongue virus (BTV) is an economically important arbovirus of ruminants transmitted by Culicoides biting midges. Vector control using residual spraying or application to livestock is recommended by many authorities to reduce BTV transmission; however, the impact of these measures in terms of both inflicting mortality on Culicoides and subsequently upon BTV transmission is unclear. This study consisted of a standardized World Health Organization laboratory assay to determine the susceptibility of European Culicoides species to deltamethrin and a field trial based upon allowing individuals of a laboratory strain of Culicoides nubeculosus Meigen to feed upon sheep treated with Butox 7.5 pour-on (a deltamethrin-based topical formulation). Susceptibility in the laboratory trial was higher in colony C. nubeculosus (24-h LC90 = 0.00106%), than in field populations of Culicoides obsoletus Meigen (24-h LC90 = 0.00203%) or Culicoides imicola Kieffer (24-h LC90 = 0.00773%). In the field, the pour-on formulation was tested with a total of 816 C. nubeculosus specimens fed upon on the thigh of treated sheep. The study revealed a maximum mortality rate of 49% at 4 d postapplication, and duration of lethal effect was predicted to be as short as 10 d, despite testing being carried out with a highly susceptible strain. The reasons for this low efficacy are discussed with reference both to the potential for lack of spread of the active ingredient on the host and feeding patterns of the major potential vector species on the sheep host. Practical implications for vector control strategies during BTV incursions are also detailed.

Management of North American Culicoides Biting Midges: Current Knowledge and Research Needs

“…Treatment caused mortality to midges for 35 days or more, but mortality never reached 100%. Venail et al (2011) showed that Culicoides spp. were quite susceptible to deltamethrin in the lab.…”

Mechanistic model for predicting the seasonal abundance of Culicoides biting midges and the impacts of insecticide control

“…Insecticides applied to host animals have shown some potential for causing high mortality in host-seeking females. A recent study determined the susceptibility of European Culicoides species to deltamethrin in a field trial consisting of a pour-on formulation of the insecticide applied to sheep [18]. They found a maximum mortality rate of 49% at 4 days post-application, and duration of lethal effect was predicted to be as short as 10 days, with susceptibility differences for the different Culicoides species.…”

The repellent effect of organic fatty acids on Culicoides midges as determined with suction light traps in South Africa

“…permethrin (Stevens et al, 1988;Mullens et al, 2000), fenvalerate pyrethroid (Holbrook, 1986), cypermethrin (Papadopoulus, 2010) and alphacypermethrin (Papadopoulos et al, 2009), have shown significant negative effects on colonyreared Culicoides (Monoculicoides) sonorensis Wirth and Jones and Culicoides (Monoculicoides) nubeculosis Meigen. Susceptibility to deltamethrin was found to be higher in colony reared C. nubeculosus, than in field populations of Culicoides (Avaritia) obsoletus Meigen or Culicoides (Avaritia) imicola Kieffer (Venail et al, 2011). In bioassay determinations of the efficacy of permethrins against C. sonorensis it was shown that midges 3 were able to feed, and thus potentially transmit pathogens, before being incapacitated (Mullens et al, 2000).…”